Phosphorus Facts (Atomic Number 15 or Element Symbol P)

Chemical & Physical Properties of Phosphorus

Isolated blackboard with periodic table, Phosphorus

michaklootwijk / Getty Images

Phosphorus is a reactive nonmetal with element symbol P and atomic number 15. It is one of the essential elements in the human body and is widely encountered in products such as fertilizers, pesticides, and detergents. Learn more about this important element.

Phosphorus Basic Facts

Symbol: P

Atomic Weight: 30.973762

Discovery: Hennig Brand, 1669 (Germany)

Electron Configuration: [Ne] 3s2 3p3

Word Origin: Greek: phosphoros: light-bearing, also, the ancient name given the planet Venus before sunrise.

Properties: The melting point of phosphorus (white) is 44.1°C, boiling point (white) is 280°C, specific gravity (white) is 1.82, (red) 2.20, (black) 2.25-2.69, with a valence of 3 or 5. There are four allotropic forms of phosphorus: two forms of white (or yellow), red, and black (or violet). White phosphorus exhibits a and b modifications, with a transition temperature between the two forms at -3.8°C. Ordinary phosphorus is a waxy white solid. It is colorless and transparent in its pure form. Phosphorus is insoluble in water, but soluble in carbon disulfide. Phosphorus burns spontaneously in air to its pentoxide. It is highly poisonous, with a lethal dose of ~50 mg. White phosphorus should be stored under water and handled with forceps. It causes severe burns when in contact with skin. White phosphorus is converted to red phosphorus when exposed to sunlight or heated in its own vapor to 250°C. Unlike white phosphorus, red phosphorus does not glow or burn in air, although it still requires careful handling.

Uses: Red phosphorus, which is relatively stable, is used to make safety matches, tracer bullets, incendiary devices, pesticides, pyrotechnic devices, and many other products. There is a high demand for phosphates for use as fertilizers. Phosphates are also used to make certain glasses (e.g., for sodium lamps). Trisodium phosphate is used as a cleaner, water softener, and scale/corrosion inhibitor. Bone ash (calcium phosphate) is used to make chinaware and to make monocalcium phosphate for baking powder. Phosphorus is used to make steels and phosphor bronze and is added to other alloys. There are many uses for organic phosphorus compounds.

Biological Activity: Phosphorus is an essential element in plant and animal cytoplasm. In humans, it is essential for proper skeletal and nervous system formation and function. Phosphate deficiency is called hypophosphatemia. It is characterized by low soluble phosphate levels in serum. Symptoms include disruption of muscle and blood function due to insufficient ATP. An excess of phosphorus, in contrast, leads to organ and soft tissue calcification. One symptom is diarrhea. The estimated average requirement for dietary phosphorus for adults age 19 and older is 580 mg/day. Good dietary sources of phosphorus include meat, milk, and soy beans.

Element Classification: Non-Metal

Phosphorus Physical Data

Isotopes: Phosphorus has 22 known isotopes. P-31 is the only stable isotope.

Density (g/cc): 1.82 (white phosphorus)

Melting Point (K): 317.3

Boiling Point (K): 553

Appearance: white phosphorus is a waxy, phosphorescent solid

Atomic Radius (pm): 128

Atomic Volume (cc/mol): 17.0

Covalent Radius (pm): 106

Ionic Radius: 35 (+5e) 212 (-3e)

Specific Heat (@20°C J/g mol): 0.757

Fusion Heat (kJ/mol): 2.51

Evaporation Heat (kJ/mol): 49.8

Pauling Negativity Number: 2.19

First Ionizing Energy (kJ/mol): 1011.2

Oxidation States: 5, 3, -3

Lattice Structure: Cubic

Lattice Constant (Å): 7.170

CAS Registry Number: 7723-14-0

The glow of phosphorus in air is chemiluminescence and not phosphorescence.
The glow of phosphorus in air is chemiluminescence and not phosphorescence. cloverphoto / Getty Images

Phosphorus Trivia:

  • Hennig Brand isolated phosphorus from urine. He kept his process a secret, choosing instead to sell the process to other alchemists. His process became more widely known when it was sold to the French Academy of Sciences.
  • Brand's technique was replaced by Carl Wilhelm Scheele's method of extracting phosphorus from bones.
  • The oxidation of white phosphorus in air produces a green glow. Although the term "phosphorescence" refers to the element's glow, the true process is oxidation. The glow of phosphorus is a form of chemiluminescence.
  • Phosphorus is the sixth most common element in the human body.
  • Phosphorus is the seventh most common element in the Earth's crust.
  • Phosphorus is the eighteenth most common element in seawater.
  • An early form of matches used white phosphorus in the match head. This practice gave rise to a painful and debilitating deformation of the jawbone known as 'phossy jaw' to workers when over-exposed to white phosphorus.

Sources

  • Egon Wiberg; Nils Wiberg; Arnold Frederick Holleman (2001). Inorganic chemistry. Academic Press. pp. 683–684, 689. ISBN 978-0-12-352651-9.
  • Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Ed.), Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4.
  • Hammond, C. R. (2000). "The Elements". in Handbook of Chemistry and Physics (81st ed.). CRC press. ISBN 0-8493-0481-4.
  • Vanzee, Richard J.; Khan, Ahsan U. (1976). "The phosphorescence of phosphorus". The Journal of Physical Chemistry. 80 (20): 2240. doi:10.1021/j100561a021
  • Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. pp. E110. ISBN 0-8493-0464-4.